In the control of a heating system for a residence, office or other building, it is common to install a thermostat on an inner wall which is located within an area where there is good air circulation. Usually, the thermostats provide for selecting a temperature within an effective control range of between 55.degree. or 60.degree. F. and 85.degree. or 90.degree. F. It is also common for many of the more recent thermostats to incorporate an internal heating element, referred to as a "heat anticipator", to provide advance heating of the bimetallic temperature sensing element and thereby prevent "overshooting" of the desired temperature level selected on the thermostat. Typical examples of thermostats incorporating heat anticipators, are disclosed in U.S. Pat. No. 3,015,447, 3,098,138, and 3,339,043.
It is frequently desirable to provide for maintaining the ambient air temperature in a house or other building at a level below the effective temperature control range of the thermostat. For example, when a newly constructed house or other building will remain unoccupied for a period of time during the winter, it is desirable to maintain the temperature of the air within the house or building slightly above freezing or between 35.degree. F. and 40.degree. F. to prevent the water pipes from freezing while minimizing the fuel consumed. Such a low ambient temperature is also desirable when an existing residence remains vacant or unoccupied for an extended period of time, for example, when a vacant house is being offered for sale, or the occupants have taken an extended winter vacation.
As a result of the precision construction required of a high quality wall-mounted thermostat, it has been found that when most of the thermostats are adjusted to the lower end of the effective temperature control range, the thermostat will continue to actuate the heating system in a manner which maintains the ambient air temperature substantially above 40.degree. F., for example, between 50.degree. and 60.degree. F. Thus when the outside temperature drops below freezing, the heating system requires a significantly greater amount of fuel to maintain the ambient air temperature within the building between 50.degree. F. and 60.degree. F. than would be required to maintain the ambient air temperature between 35.degree. and 40.degree. F.